I've gotten a couple responses from people regarding my note yesterday
regarding replacing the main and rod bearings in my TR-250. Just to make
sure they make the record, in case their concerns weren't cc'd to the list,
I thought I'd share the gist of them with y'all. I do appreciate the
replies. Every bit of knowledge and advice we can gather about our cars
helps keep/put them on the road.
I said:
I found the upper bearing shells a bit tricky to remove and insert. You
just have to fiddle with them and turn the crank to remove the old
ones. Oil both sides of the new shells.
to which Mike Jeffreys replied:
Assuming David H. doesn't get here first, I pass on his previous message
on this item; with which I concur:
"Just a warning here. When replacing main bearings like this, use lots
of oil on the "bearing surface", but NO oil on the backing
sides. Bearings should be applied dry to bearing caps and the block
face. Heat transfer is of utmost concern, so metal-to-metal contact must
be as perfect as possible. Once the bearings are installed, then lots of
oil (or a lithium "white" grease) can be applied to the "moving"
surface."
I have no particular opinion on this one way or 'tother, only to note that
there is not a ton of clearance between the crankshaft and the block when
replacing the bearings the way I did. (I did not notice the crank had moved
at all when I removed the main bearing caps.) There is such a thin film of
oil between the shell and the block, especially after you torque everything
down, I doubt it would be significant. Finally, motor oil's heat transfer
properties are pretty good, aren't they? As I pointed out to Mike, only the
four main bearing shells between the crank and the block got the backside
oil treatment. The other 16 shells were inserted dry.
I said:
filled it up with oil, and cranked it. No oil pressure. Hmmm. Look
underneath to see where the oil must be spilling out. Crank it some
more. Look underneath again. Crank it some more. Finally, the oil
pressure shot up and engine revs tailed off. Now, stop and put the plugs
in, roll it out of the garage, and fire it up.
To which Dan Parslow replied:
Are you guys remembering to prime the oil pump at reassembly? This, I'm
told, is crucial. (Hain't rebuilt an engine yet myself.)
My intent in cranking the engine with the plugs removed was to prime the oil
pump. By cranking without the points, I figured to spin the bearings with as
little load as possible. Nothing else (cam, rockers, valves) got replaced,
so they had the usual amount of old oil coating their surfaces. Short of
removing the distributor and cranking the pump using a drill (is there a
tool to chuck in your drill for this purpose?) I could see no other
practical way to prime the pump. Had I installed a spin-on oil filter
adaptor (I may well at the first oil change), I would have filled the filter
with oil before installing it, just to lessen the time before oil began
circulating in the engine.
Thanks again for the responses. It's great to have this resource to draw on.
If my bearings fail, you'll be the first to know. :-)
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